I recently wanted to play around with Android development, but I didn’t have any Android devices. So I picked up a cheap Android tablet from Walmart. It’s an RCA Viking Pro 10.1″ running Android 6.0. The model number is RCT6303W87M, although in software it identifies itself as RCT6303W87M7. But…Walmart’s website says it’s an RCT6303W87 DKF. I have no idea what is really correct, but I figured I would write out all of the model numbers so that people from Google can find this post.

Anyway, I realized after I bought it that the micro-USB port is strictly for charging. Oops, my bad. It turns out that this tablet wasn’t really designed with USB connectivity as a device in mind. It does have a USB type A port, but that’s for connecting other devices to the tablet, not the other way around. I tried turning on developer mode and any options on the tablet I could find, but nothing allowed connectivity with the computer.

I did some Googling, which seemed to indicate that other people had been in this predicament. There was talk of a mysterious “special cable” that RCA provides as an option to buy. I also found people discussing using a USB A-to-A cable with varying levels of success. I decided the best thing to do would be to contact RCA support, which led me down a bit of a rabbit hole.

The friendly RCA support person told me I needed to buy a special cable, and gave me a link on RCA’s store to order it, along with instructions for using the cable — in particular you have to connect the cable while the tablet is off, and the blue end needs to be plugged into the tablet. The cable had a price tag of $5 on their store, but it looked just like a standard USB A-to-micro cable that everyone has laying around. I went ahead and ordered it anyway, but sure enough, it wasn’t actually a special cable. It was just a run-of-the-mill micro USB cable, which I had already tried myself. There wasn’t a blue end — the entire cable was black. To make matters worse, the cable came from Canada, so I had to overpay for shipping, not to mention the foreign transaction fee on my credit card.

I wrote back to RCA support. The same person who helped me first time apologized and indicated that I hadn’t actually ordered the special cable. It appears that the special cable is available from RCA, but it’s not publicly available on their site so you have to do a special order to get it. So this time RCA sent the correct cable my way for no additional charge.

Today the cable arrived, and it is indeed special. It’s a USB A-to-A cable (well…since it came from Canada, maybe we should call it an eh-to-eh cable?). The ends are clearly marked so you know which end goes to the tablet and which end goes to the computer, and the tablet’s end is blue (although you can’t see it in the picture, because the part that goes into the computer is the part that’s blue, like a USB 3.0 cable).

I don’t know if there’s anything special about the cable over other A-to-A cables. The blue end that goes to the tablet appears to be a USB 3.0 connector, which makes sense because USB 3.0 cables are typically blue. So there are extra pins for USB 3.0–but the tablet itself doesn’t actually have connections for any of those pins. I dunno. It’s a mystery. I think they just used a 3.0 connector so they could get one that is colored blue. I think there must be something special about the cable other than just being an A-to-A cable; why else would they mark which end is which? I don’t have an easy way to do any further tests on the cable to try to figure out which pins are connected to which pins.

I guess you could say I made out like a bandit, because the special cable would cost $15 according to the label on the package. The label indicates the product is a “special cable” and it’s for the RCT6513W87, so I assume that tablet has the same problem. For reference for readers, here are the instructions RCA provided me for using the cable:

  1. Tablet has to be completely off
  2. Connect the special cable from tablet to computer, please note that the blue end goes to the tablet
  3. Plug the AC adapter into the tablet
  4. Turn on the tablet
  5. Open My Computer to see if PC will recognize the device, if not, please proceed to the next step
  6. Open Device Manager on your PC
  7. Choose Portable Devices and select Upgrade Driver Software
  8. Click on browse my computer for driver software
  9. Select “Let me pick from a list of a device drivers on my computer”
  10. Go to Portable Device and choose MTP USB Device

As soon as you do this, your PC should recognize the tablet. [In] some instances, if [your] PC will not recognize the device again, you may have to [go] through the instruction[s] above.

I can confirm that if you start with the tablet turned off and then plug in the cable, it does seem to work properly and enumerate as a USB device on the computer as soon as you turn the tablet on. It worked out of the box with Android SDK on Linux. If you unplug the USB cable, you do end up having to power the tablet off in order to reconnect the USB, so if you do Android debugging, it would be smart to set up Wi-Fi debugging using the steps on this StackOverflow answer.

Hope this helps someone out there!

At work, I was trying to restore a Lenovo IdeaPad Z510 back to the factory default configuration after Ubuntu Linux had been installed on it. I wanted to restore it back to the factory default Windows 8.1 scheme. I noticed that Lenovo had a “One-Key Recovery” (OKR) option, so I decided to try it. I pressed the NOVO button and chose the system recovery option. When I tried to run system recovery, it gave me this error message:

The program cannot restore the system partition because its structure is incorrect. You may have to recreate the partition to continue.

I wasn’t the one who set the laptop up originally, but I was pretty sure that since Ubuntu was installed, it had changed something about the partition layout and broken something. So I booted into an Ubuntu Live USB stick and used GParted to check it out. Sure enough, a few extra partitions had been created for ext4 and swap. It appeared that the main Windows partition had been shrunk, and the extra Linux partitions had been created in the space made available. I deleted the extra Linux partitions and resized the main Windows partition to fill up the available space.

Unfortunately, that still didn’t fix it. Maybe it would in some people’s cases, but something was still wrong with the partition layout. I started digging into the recovery partitions on the laptop’s hard drive and found a file that contained info about the partition layout. It was on the partition called PBR_DRV, and the path to it was OKRBackup\Factory\Info.ini. This file contained info about the location, size, and options for each partition.

I was able to use the information in this file, combined with the “gdisk” command while booted into an Ubuntu Live USB, to fix everything. It turned out that all of my partitions were the correct size, but the “Attributes” from this file didn’t match — several of the partitions were missing the “don’t automount” flag.  I was able to use gdisk to set that flag on partitions that needed it in the expert menu. Also, for some reason, the MSR partition had been deleted, so I was able to recreate it (I created it as a new unformatted partition and set the label in GParted) and set the proper “Id” and “Type” GUID values using gdisk as well. I don’t know if Ubuntu deleted it, or if the person who installed Ubuntu manually deleted it.

For some reason, the partitions were numbered incorrectly after I did all of this, so I was able to use the “sort” function in gdisk to number the partitions properly afterward.

After I confirmed that the labels, locations, sizes, “Id”/”Type” GUIDs, and attributes all matched between Info.ini and the actual disk, I saved my changes to the partition table and tried running the system recovery. This did the trick and everything worked fine!

I didn’t write down paths or anything while I was doing this, and I had to do some Googling to find the names again, so I might be slightly off on some of the filenames. But what I described is pretty much what I did. For future reference, I did write down the following information about the partitions, in case anybody might find this useful:

  • sda1: WINRE_DRV
    • Start sector = 2048
    • End sector = 2050047
    • Size = 1000 MB
  • sda2: SYSTEM_DRV
    • Start sector = 2050048
    • End sector = 2582527
    • Size = 260 MB
  • sda3: LRS_ESP
    • Start sector = 2582528
    • End sector = 4630527
    • Size = 1000 MB
  • sda4: MSR
    • Start sector = 4630528
    • End sector = 4892671
    • Size = 128 MB
  • sda5: Windows8_OS
    • Start sector = 4892672
    • End sector = 1874599935
    • Size = 891.55 GB
  • sda6: LENOVO
    • Start sector = 1874599936
    • End sector = 1927028735
    • Size = 25 GB
  • sda7: PBR_DRV
    • Start sector = 1927028736
    • End sector = 1953523711
    • Size = 12.63 GB

After I upgraded Ubuntu MATE from 16.04 to 18.04, I noticed a really annoying behavior. Clicking in the empty area of a scrollbar (between the handle showing where your current position is and the up or down arrow) used to scroll up or down a page at a time. After the 18.04 upgrade, this behavior changed, and now it moves the handle directly to the position where you clicked. Some people like this, some people don’t. I don’t. Unfortunately, they didn’t decide to make this a configurable option in the graphical settings for some strange reason.

It turns out that this is actually a GTK 3 behavior — it’s caused because MATE recently changed to use GTK 3. Luckily, it’s an easy fix:

Go into the directory of the theme you are currently using. So for my current configuration, I went into this directory:

/usr/share/themes/Ambiant-MATE/gtk-3.0

Edit the “settings.ini” file. Add the following line to the bottom of it:

gtk-primary-button-warps-slider = false

Log out and back in, and you’re done.

After upgrading my machines from Ubuntu MATE 16.04 to 18.04, I noticed that something was subtly wrong with my top menu/panel: the network notification icon was missing. Something about the 16.04 to 18.04 upgrade process broke it. It happened on both of the machines I upgraded, so I don’t think it was a random thing that only I was experiencing.

Note: my fix for this will reset your panel layouts, so take a screenshot and/or save any info about the layout of your panels before following the steps below so you will have a reference for restoring it back the way you want it afterward.

To start out, I will share some background info: if you are used to the default menu layout of the top panel with the Applications, Places, and System menus, they decided to change this in 18.04. That layout is called “Traditional”, and Ubuntu MATE 18.04 now defaults to a new layout called “Familiar”. I personally don’t like the Familiar layout because it doesn’t have the Places menu, but I guess enough people liked it that they wanted to make it the default.

Anyway, the fix for this is to reset your panel to one of the default configurations, which will add everything back properly. But like I said in bold above, it will also erase any customizations you have done. Here’s the fix:

  1. Open up MATE Tweak. In the Traditional layout, it’s in the System -> Preferences -> Look and Feel menu.
  2. In MATE Tweak, click on the Panel category.
  3. In the top dropdown menu, choose the layout you want. To match Ubuntu 16.04’s default, choose Traditional. To match Ubuntu 18.04’s default, choose Familiar.
  4. Confirm that you want to change the layout by clicking OK.
  5. All done! Your network notification icon should be restored, and now you can reapply any of your customizations to the panel.

Another way to fix it is to right-click on the panel and choose Reset Panel, but I think the method I described above is better because it lets you pick which layout you want to start from.

I recently upgraded a couple of my machines from Ubuntu MATE 16.04 to 18.04. On both of them, I noticed that after the upgrade, the login window did not look correct. There was no background image. It didn’t look like a fresh 18.04 install. Plus, any changes I did in the Administration -> Login Window program didn’t take effect. I did some digging, and figured out what was going on.

Sometime between 16.04 and 18.04 (it appears that this happened starting in 17.10), Ubuntu MATE decided to stop using lightdm-gtk-greeter, and instead switched to using slick-greeter. It seems to be that on update installs, lightdm-gtk-greeter is not being removed, so it’s defaulting to using it rather than slick-greeter.

I was able to solve this very easily by running the following command:

sudo apt purge lightdm-gtk-greeter

After that, I logged out, and Ubuntu MATE’s correct login screen appeared. It’s as simple as that!

At work, we still have a Windows 98 computer that we use for programming a few very old products that we no longer sell but still support. I tried to do some research so we could move this process onto a newer computer, but I wasn’t able to find a suitable tool. Thus, I’m stuck maintaining a Windows 98 computer until we no longer have to support the product. I do any necessary development work on a different computer, but I still need to get the program binaries onto the Windows 98 machine. The computer doesn’t have a floppy or CD drive, and Windows 98 didn’t come with a USB mass storage driver. Honestly, all of those solutions would be inconvenient for me anyway.

It’s super insecure, but you can enable file sharing on the Windows 98 computer and connect to it from Linux. Programming binaries to old microcontrollers is literally the only thing this computer is used for, so I’m not too concerned about the security pitfalls of SMB.

There are several tools designed for accessing an SMB share from Linux. Most modern desktop environments provide an interface to access Windows file shares. From the command line, I have used smbclient from Samba, which also works great in most situations. When we recently added subnets to our work network and the Windows machine was on a different subnet from my development machine, I had to come up with a solution to connect to it because it no longer showed up automatically. I didn’t want to set up a WINS server to enable cross-subnet Windows file sharing just for this one little application. I couldn’t get smbclient to connect to the Windows 98 computer properly across subnets in this scenario, so this blog post will focus on how to use Linux’s built-in CIFS support so you can use the standard “mount” command, which does work across subnets if you do it right.

First of all, you will need to ensure you have mount.cifs installed. In Ubuntu 16.04, you can type the following command to install it:

sudo apt install cifs-utils

Here is a sample mount command:

sudo mount -t cifs //192.168.2.7/MYSHARE /tmp/windows -oservern=MYSERVER,guest,vers=1.0

Here is an explanation of each parameter:

  • -t cifs
    • This specifies to the mount command that we’re trying to mount a CIFS share.
  • //192.168.2.7/MYSHARE
    • This is the SMB server and share you are trying to mount. 192.168.2.7 is the IP address of the server. MYSHARE is the name of the share on the server. Note that I am using forward slashes here, not backslashes like you would expect on Windows.
  • /tmp/windows
    • This is the local directory to mount the share on. Make sure you create the directory before trying to run this command.
  • -oservern=MYSERVER…
    • “-o” specifies options. Everything following is a comma-separated list of options:
    • servern=MYSERVER
      • This option specifies that the name of the server you are connecting to is MYSERVER. You have to specify the name of the server you’re trying to connect to if you try to mount a Windows 98 share, or else it won’t work. So this option is super important.
    • guest
      • This specifies that we’re trying to connect as a guest. Otherwise, you can use the username= and password= options. It’s probably not a good idea to use the password= option though, because it leaves your password visible in plain text; there is a credentials= option that works a lot better by letting you specify a filename containing credentials.
    • vers=1.0
      • This tells the kernel to use the SMBv1 protocol. It used to be the default before Linux 4.13 came out, but now Linux defaults to a newer protocol for security reasons.

There are many other parameters that you may need to use for various reasons. You can get information about all of the available parameters by typing this command into your terminal:

man mount.cifs

Note that prior to Linux 4.13, I did not have to specify the protocol version as 1.0. It just worked. But with Linux 4.13 and later, it defaults to a newer protocol version for security reasons. If you try to connect to a Windows 98 share without specifying protocol version 1.0, the mount command will hang and eventually fail. I was able to determine what was going on by looking at a Wireshark trace, which then led me to the mount.cifs manpage to discover how to specify an older protocol version.

I have noticed that if you try to replace an existing file, you will get an error. So in my experience, you have to delete the existing file first. This is not a big deal in my use case.

To unmount it when you’re done:

sudo umount /tmp/windows

Hope this helps someone out there!

If you can believe it, Mac OS X 10.4 “Tiger” is over 12 years old as of this writing. It was first released in April of 2005. It was also the version that Apple first used on its Intel Macs in 2006. Because the Intel version came out in 2006 after the PowerPC version had already been in stores, it’s kind of a weird release. There wasn’t a retail copy of the Intel version of Tiger. It was only bundled with the first Intel Macs before 10.5 “Leopard” came out in 2007.

Because of the way it was weirdly released, it’s not super common to virtualize OS X 10.4 for Intel. Nobody’s really using it anymore because it’s so old. It’s probably full of security holes. And technically, it’s against OS X’s license agreement to virtualize it (same with the non-server versions of 10.5 and 10.6). With that said, I really doubt Apple cares about such an old version of OS X these days, and I think creating a VM of it is a really cool thing to do for educational purposes. Who knows — maybe it’s still useful for certain developers who still need to test how things work on 10.4 without keeping an old power-hungry machine around that is capable of running it.

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As soon as you add a USB host port to your microcontroller project, a lot of possibilities suddenly open up. You can add support for plugging in a flash drive for firmware updates, diagnostics, and all kinds of miscellaneous data transfer. One task I’ve needed to complete in the past is the ability to save an Excel .xls spreadsheet. After doing some research, I found that this was actually a fairly difficult task on a microcontroller with limited memory. Most of the C/C++ Excel libraries I’ve found aren’t prepared to work in a microcontroller environment, and they generally do dynamic memory allocation because, well, Excel files are dynamically sized.

I’m going to assume that you already have USB mass storage support figured out for your particular project. This will usually involve using a USB library that provides the USB functionality. Many USB libraries also provide support for accessing mass storage devices. On top of this, you will also need a filesystem library for accessing a FAT32 filesystem, which is arguably the most common filesystem in use on flash drives today. One library I would recommend for working with FAT32 filesystems is FatFS. Note that FatFS doesn’t provide any of the USB functionality — you will have to hook it up to your USB library in diskio.c.

Now, back to the actual file generation. One thing you can do is simply generate a .csv file instead. That strategy works pretty well, and it may end up being all that you need for your particular project. One downside is that in certain cases, it will bring up a dialog box that forces the user to specify options for importing the file. LibreOffice is a particular offender in this regard.

I wanted a solution that generated a real .xls file that Excel and LibreOffice could open without any prompting and didn’t require the use of malloc(). I ended up writing my own library called MicroXLSWriter. MicroXLSWriter is a simple library that should fit on any embedded system. It generates files in a very old .xls format (BIFF2, from Excel 2.0). Modern versions of Excel (tested through Office 2007) can still open BIFF2 files without any problems. My code doesn’t completely follow the BIFF2 format perfectly, but it’s good enough that Excel and LibreOffice don’t seem to complain.

MicroXLSWriter is very limited. It doesn’t support any cell formatting or styles. You can’t customize fonts, colors, borders, or anything like that. The only thing it lets you do is set the width of each column and put text or a number into each cell. For what I needed, this is completely fine. BIFF2 files aren’t typically supported by .xls manipulation libraries, so if you’re generating something that won’t simply be opened by a user with Excel or LibreOffice, you should probably look elsewhere — if you can find a better alternative that still fits in a microcontroller.

If you’re interested, try it out. The source code is on GitHub and it has a very permissive 2-clause BSD license that allows you to use it in whatever commercial or open-source project you want, as long as you follow the simple requirements about preserving the copyright notice in materials distributed with your project (e.g. documentation). If you get a chance, let me know if you use it! I’m curious to hear about various applications where it ends up being used.

For various reasons, you might end up needing to hook up your iOS device directly to an Ethernet network without using Wi-Fi. For example, maybe you’re in an area with bad Wi-Fi reception. Or perhaps you are trying to do something that requires high bandwidth and your Wi-Fi access point doesn’t have the best speed.

Well, it turns out that iOS has supported Ethernet for a while. Obviously your iOS device doesn’t have an Ethernet port, so you have to use a USB-to-Ethernet adapter. As of iOS 10.2, there is even a settings screen that appears when you plug in a supported adapter. Older versions of iOS apparently still supported Ethernet, but didn’t provide a screen for setting it up, so you were probably stuck with the default settings (grabbing an IP address from a DHCP server). Now that there is a setup screen, you can configure it exactly how you want.

I tested it out with three devices tonight, and they all worked flawlessly: iPhone 6, iPhone 7, and iPad Air.

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I recently ran into a problem upgrading a computer from Windows 7 to Windows 10. I received an error message with the following error code: 0x800703ed

It turns out this system was a dual-boot Linux and Windows system. I was actually booting to a different hard drive which had GRUB installed, and then GRUB was booting to my Windows drive. I fixed the problem by switching my BIOS boot order to boot directly to the drive with Windows 7 installed and then repeated the update process. This resulted in a successful Windows 10 upgrade. After the upgrade was complete I was able to change my BIOS boot order back to the way it was before, and now everything works fine.